Slaves were recognized on the Hill with plaques in the new visitor center's Emancipation Hall and outside the galleries to the Senate and House chambers following a study by a congressional task force led by civil rights icon Rep. John Lewis (D-Ga.).

"It was a shameful omission that visitors to the Capitol could tour the building to learn its history but not learn that slave labor was used in its construction," argued Rep. Gary Ackerman (D-N.Y.) in a statement. "I'm proud Congress took action to correct this failure and I now urge the White House follow suit."

There is extensive documentation of the slaves' role in building the commander-in-chief's residence. Ackerman said he was inspired to look into slave labor at the White House by one of his constituents, Mandingo Tshaka, an activist from Queens, N.Y., whom Ackerman credited with educating people about slaves' experiences on Capitol Hill.

"Slaves helped dig the foundation for the White House," Ackerman wrote in a letter to the White House Thursday. "They quarried stone that would be used for the walls, dug up clay for thousands of bricks, cut timber, sawed lumber, and performed carpentry inside the White House. Even after White House construction was completed, slaves continued to support White House operations. Slaves served in White House domestic staff from 1800 through the Civil War."

In a country that names freedom as its top value, Ackerman argued that history should be acknowledged.

"From the U.S. Capitol Building to the White House, our national symbols that represent freedom to so many of us, were built by people who were anything but free," Ackerman wrote. "While the larger injustice of slavery can never be adequately corrected, the continuing failure of properly informing visitors to Washington of the history of slaves building our national structures--including the White House--should be remedied."